The Black Friday app, available for the Android and the iPhone, lets you browse through different stores, and even check out ads that have been leaked.
TGI Black Friday is a similar option. Along with letting you peak at leaked ads, you can also sign up for push notifications when new ones are posted.
Both let you add items to a virtual shopping list.
Once at the store, if you're unsure of the bargain you're getting compare prices by scanning the item's barcode with the Snaptell app.